Hole Transport Layer Microroughening for Waveguide Mode Extraction in Organic Light‐Emitting Diodes

Abstract

Herein, simple and scalable approach to enhance the out‐coupling efficiency in organic light‐emitting diodes (OLEDs) is presented. By exposing the 4,4′‐bis[N‐(1‐naphthyl‐1‐)‐N‐phenylamino]‐biphenyl (NPB) hole transport layer to hydrofluoroether (HFE) solvent for several minutes, a controllable microroughening of the film is achieved, which results in the formation of random scattering centers in the OLED structure. Optimized NPB microroughening for phosphorescent OLED with Ir(ppy)3 emitter leads to luminous efficacy improvement of 23% (from 64 to 79 lm W−1 at 1000 cd m−2) without additional external out‐coupling. Angular resolved spectroscopy of the OLED with an internal scattering layer reveals constant color almost independent of the viewing angle and Lambertian intensity distribution.